WCAG Reference

Text needs a contrast ratio of at least 4.5:1 against its background. Large text - 24px or 18.5px bold and above - can drop to 3:1.

Text needs a contrast ratio of at least 7:1 against its background. Large text - 24px or 18.5px bold and above - can drop to 4.5:1.

Non-text UI components and graphical objects need a contrast ratio of at least 3:1 against adjacent colours.

There's no WCAG success criterion that says "text must be at least X pixels." But text size directly affects readability and contrast perception, and WCAG references size thresholds in several places.